ok have almost new gen VI 454's in my gibson, 100hrs, now these things never see 4k, the other weekend put the boat on plane, hit about 2k was laying down, missing sputtering, etc. stopped pulled fuel filter..was plugged, replaced, figured good to go..no diff...changed water seperator..no diff, running delco EST dist(stock crusader) swapped modules, rotors, coil wire, has 5 psi fuel pressure at carb, swappped carbs, nothing has made any diff, also pulled dist and replaced the pick-up coil in there...tried new coil, and dist cap..run fine at idle, sometimes runs up to 2500 before going to crap..sometimes only 2000 and will do it without a load on it....have just about tried everything I know of ?? any body ?? thanks for any help...Rob

5psi ... shouldn't it be atleast 7

Had a 20' inboard in my younger days. Had pretty much the same problem. The brass fuel line adapter at the top of the fuel cell had a screen under it that was full of trash.Cleaned it out boat ran fine. Keep us posted. Gus

Did you look at the check valve in the tank? Just a thought.

Fuel pressure should be at least 7psi. Weak fuel pumps? At 5 psi you're probably draining the bowls at 2500 rpm.

no, have checked the fuel pressure before, elec pumps w/ regulators set @ 5 psi, only running 600 edelbrock carbs, been at that pressure since the repower 2 seasons ago...removed the anti-siphon valves a couple of years ago, fuel pressure steady..also have clear fuel filters before the carbs, stay full, also the engine will do it on a free rev in neutral, would not have time to drain the float bowl in 5 seconds...weird I know..

have you tried another distributor all together? worked on one recently with the same problem. sometimes it doesn't take much to throw off the signal. at least try and borrow one if you can. if i had to guess i would say this is your problem.

I broke the roll pin in the distributor gear once before and had similar issues. It still appeared that it was still there but was broken.
Just a thought

roll pin fine, just had the dist shaft out replacing the pick-up coil, and had a new dist to try this weekend..the only part of the dist not changed is the shaft and I know the magnetic wheel can go bad..so thats my next thing to try.....getting pretty old at this point...thanks for all the help...Rob

I am having a similar problem with both my engines. Runs fine at idle, but when throttling up aound 2500 rpm enigines break up, like its dropping cylinders. Have had two mercruiser techs look at it so far, and they both have no idea what it could be. I few local people have told me that this year they have heard a lot of peole having fuel problems. Going to try and use some Star-Tron and see what happens, before I start changing everything out like you just did. Already did fuel filters, cap, rotor, wires and plugs.